Typically in power systems, gas circuit breakers are employed to perform current switching, including in the case of excessive fault current. In the common puffer type of gas circuit breaker, the arc discharge is extinguished by directing arc-extinguishing gas onto the arc.
An example is to be found in issued Japanese Patent Number Tokko H 7-109744 (hereinafter referred to as Patent Reference 1). A specific description of such a puffer type gas circuit breaker is given below with reference to FIG. 6A, FIG. 6B, and FIG. 6C. FIG. 6A to FIG. 6C show a rotationally symmetrical shape whose axis of rotation is the center-line: FIG. 6A is the conducting condition; FIG. 6B is the earlier half of the current interruption action; and FIG. 6C is the latter half of the current interruption action.
As shown in FIG. 6A to FIG. 6C in a puffer type gas circuit breaker, there are provided a facing arc electrode 2 and a facing powered electrode 3; opposite to and on a concentric axis with these electrodes 2 and 3, there are arranged a movable arc electrode 4 and movable powered electrode 5 in a freely reciprocable manner. These electrodes 2 to 5 are accommodated in a sealed enclosure (not shown) that is filled with arc-extinguishing gas 1. As the arc-extinguishing gas 1, SF6 gas (sulfur hexafluoride gas), which is of excellent arc interruption performance (extinguishing performance) and electrical insulating performance, is usually employed; however, other media could also be employed.
The movable arc electrode 4 is mounted at the tip of a hollow drive rod 6; the movable powered electrode 5 is mounted at the tip of a puffer cylinder 9. Also, an insulated nozzle 8 is mounted on the inside of the movable powered electrode 5, at the tip of the puffer cylinder 9. This movable arc electrode 4, movable powered electrode 5, drive rod 6, insulated nozzle 8 and puffer cylinder 9 are integrally constituted. These integrally constituted parts are driven together with the movable-side electrodes 4, 5 and so will be referred to in common as a movable section. Also, a fixed piston 15 is freely slidably arranged in the puffer cylinder 9. The fixed piston 15 is fixed within the sealed container independently of the aforementioned movable section. An inlet hole 17 and inlet valve 19 are provided in the fixed piston 15.
A puffer chamber 22 is constituted by the space that is defined by the drive rod 6, puffer cylinder 9 and the sliding face 15a of the fixed cylinder 15. The puffer cylinder 9 and fixed piston constitute means for pressurizing the arc-extinguishing gas 1 in the puffer chamber 22 and the puffer chamber 22 constitutes a pressure-accumulation space in which the pressurized arc-extinguishing gas 1 is accumulated. The insulated nozzle 8 constitutes means for defining (rectifying) and directing (blasting) the flow of arc-extinguishing gas 1 from the puffer chamber 22 towards the arc discharge 7.
In a puffer-type gas circuit breaker constructed as above, in the closed condition, the facing arc electrode 2 and the movable arc electrode 4 are mutually connected and in current-conducting condition, and the facing powered electrode 3 and the movable powered electrode 5 are mutually connected and in current-conducting condition (see FIG. 6A). When current interruption action is executed from this closed condition, the movable arc electrode 4 and the movable powered electrode 5 are driven in the rightwards direction in FIG. 6A, FIG. 6B and FIG. 6C by the drive rod 6.
When, as the drive rod 6 is driven, the facing arc electrode 2 and the movable arc electrode 4 are separated, an arc discharge 7 is generated between these arc electrodes 2, 4. Also, accompanying the interruption action, the volume in the puffer chamber 22 is reduced by mutual approach of the puffer cylinder 9 and the fixed piston 15, causing the arc-extinguishing gas 1 in the chamber to be mechanically compressed (see FIG. 6B). The insulated nozzle 8 shapes (rectifies) the flow of arc-extinguishing gas 1 that is compressed in the puffer chamber 22 and directs this flow onto the arc discharge 7 as a gas blast 21, thereby extinguishing the arc discharge 7 (see FIG. 6C).
Also, if the puffer type gas circuit breaker performs a closure action, at the time-point where the pressure of the puffer chamber 22 becomes lower than the filling pressure of the arc-extinguishing gas 1, the inlet valve 19 provided in the fixed piston 15 is operated, thereby opening the inlet hole 17, so as to replenish intake of air-extinguishing gas 1 into the puffer chamber 22. In this way, the arc-extinguishing gas 1 in the puffer chamber 22 can be rapidly replenished even during closure action immediately after current interruption. Consequently, even if the puffer-type gas circuit breaker performs a high-speed re-closure action, the arc discharge 7 can be reliably extinguished by maintaining ample gas flow rate of the gas blast 21 in the second interruption action.
However, when the puffer-type gas circuit breaker interrupts a large current, the pressure of the arc-extinguishing gas 1 in the puffer chamber 22 needs to be raised to a blasting pressure that is fully sufficient to extinguish the arc discharge 7. In these circumstances, if it is attempted to increase the blasting pressure of the arc-extinguishing gas 1 simply by using a powerful drive mechanism, because of the need to install such a powerful drive mechanism, mechanical vibration when performing the interruption action is increased and costs are also raised.
In a puffer-type gas circuit breaker, there has therefore been a demand to reduce the drive operating force while maintaining a powerful blasting pressure. In order to meet this demand, an action of elevating the pressure of the puffer chamber 22 by introduction of high-temperature hot exhaust gas 20 generated by the arc discharge 7 i.e. a so-called self-pressurizing action is utilized. A self-pressurizing action in a puffer-type gas circuit breaker is described below with reference to FIG. 6B.
Specifically, as shown in FIG. 6B, in the earlier half of the current interruption action, the facing arc electrode 2 is not fully extracted from the narrowest flow path section (throat) of the insulated nozzle 8, with the result that hot exhaust gas 20 from the periphery of the arc discharge 7 flows into the interior of the puffer chamber 22. As a result, without needing to employ a powerful drive mechanism that provides a large drive operating force, the internal pressure of the puffer chamber 22 becomes high so the blasting pressure of the gas blast 21 is maintained and a reduction in the drive operating force can be achieved.
Also, in the case of a gas circuit breaker of the type called a series puffer type gas circuit breaker (for example as disclosed in issued Japanese Patent (Tokko H 7-97466 (hereinafter referred to as Patent Reference 2), further reduction in the drive operating force can be achieved by restricting the space affected by the self-pressurizing action. As shown in FIG. 7A, FIG. 7B and FIG. 7C, a series puffer type gas circuit breaker is characterized in that the puffer chamber is divided into two spaces by a partition plate 10. It should be noted that, in FIG. 7A, FIG. 7B and FIG. 7C, members that are the same as in the puffer-type gas circuit breaker shown in FIG. 6A, FIG. 6B, and FIG. 6C are given the same reference numerals and further description thereof is dispensed with. FIG. 7A to FIG. 7C likewise show a rotationally symmetrical shape whose axis of rotation is the center-line: FIG. 7A is the conducting condition; FIG. 7B is the earlier half of the current interruption action; and FIG. 7C is the latter half of the current interruption action.
Of these two spaces into which the puffer chamber is divided, the space into which the hot exhaust gas 20 is introduced from the space where the arc discharge 7 is generated is designated as a heating puffer chamber 11 and the space where the fixed piston 15 is freely and slidably arranged on the opposite side from this is designated as a compression puffer chamber 12. A communication aperture 13 is provided in the partition plate 10 that partitions the heating puffer chamber 11 and the compression puffer chamber 12, and a non-return valve 14 is mounted therein. Also, an exhaust hole 16 and pressure relief valve 18 are arranged in the fixed piston 15. The pressure relief valve 18 is arranged to open when the pressure of the compression puffer chamber 12 rises to a predetermined set value.
In a series puffer type gas circuit breaker constructed as above, in the earlier half of the current interruption action, as shown in FIG. 7B, the facing arc electrode 2 does not completely pass through the narrowest flow path section (throat) of the insulated nozzle 8, so the hot exhaust gas 20 produced by the arc discharge 7 flows into the heating puffer chamber 11. Consequently, the pressure of the heating puffer chamber 11 is greatly elevated by the self-pressurizing action achieved by the arc heating, so a pressure that is ample for extinguishing the arc discharge 7 can be obtained and the high pressure necessary for large current interruption can be created within the enclosed space of the heating puffer chamber 11.
Thereupon, whilst the pressure of the heating puffer chamber 11 is high due to the pressure of the compression puffer chamber 12, the non-return valve 14 is passively closed by this pressure difference. Consequently, even though the pressure of the heating puffer chamber 11 is elevated, there is no possibility of the effect thereof reaching the compression puffer chamber 12, so there is no possibility of the drive force acting on the fixed piston 15, that slides through the compression puffer chamber 12, being increased. As the current interruption action proceeds, the pressure in the compression puffer chamber 12 becomes high, and when the pressure of the compression puffer chamber 12 exceeds that of the heating puffer chamber 11, the non-return valve 14 opens, allowing the arc-extinguishing gas 1 to flow into the heating puffer chamber 11 from the compression puffer chamber 12 and thus making it possible to blast the air discharge 7 with a gas blast 21 having the gas blast quantity and pressure required for current interruption.
It should be noted that the pressure relief valve 18 opens as soon as the pressure of the compression puffer chamber 12 rises to a preset value. Consequently, the pressure of the compression puffer chamber 12 is always kept below the set value i.e. only a pressure restricted by the pressure relief valve 18 is applied to the fixed piston 15. There is therefore no possibility of the pressure within the compression puffer chamber 12 becoming an excessively high pressure, which would apply a large load to the drive mechanism.
Also, in the case of interrupting a small current in a series puffer type gas circuit breaker, the self-pressurizing action produced by arc heating is small, so pressure elevation of the heating puffer chamber 11 by this action cannot be expected. Consequently, the pressure of the compression puffer chamber 12 is relatively higher than the pressure of the heating puffer chamber 11, so the non-return valve 14 is in an open condition. As a result, the arc-extinguishing gas 1 flows into the heating puffer chamber 11 from the compression puffer chamber 12 due to the compressive action of the fixed piston 15, so the necessary blasting pressure for current interruption can be guaranteed.
However, a solution to the following problems of a conventional gas circuit breaker was still awaited.
(A) Temperature of the Gas Blast
In a conventional gas circuit breaker, the hot exhaust gas 20 from the arc is introduced into the puffer chamber 22 or heating puffer chamber 11, so a gas blast 21 that is heated to a high temperature is directed onto the arc discharge 7. Consequently, the efficiency of cooling the arc discharge 7 is lowered, which may lower the circuit breaking performance.
(B) Effect of the Temperature of the Gas Blast on Durability and Maintenance
Also, the temperature in the vicinity of the arc discharge 7 is raised by the high-temperature gas blast 21 being blown onto the arc discharge 7. As a result, the arc electrodes 2, 4 and insulated nozzle 8 tend to be degraded by exposure to high temperature, giving rise to a need for frequent maintenance. This is contrary to user needs for improved durability and reduced maintenance.
(C) Current Interruption Time
In addition, it takes a certain amount of time to raise the pressure in the heating puffer chamber 11 and in the puffer chamber 22. The time required until current interruption is completed may thereby be prolonged. Since a gas circuit breaker is an appliance for rapidly interrupting excess fault current in a power system, from the point of view of the basic function of a gas circuit breaker, it is always demanded that the time that elapses before current interruption is completed should be as short as possible.
(D) Drive Operating Force
Also, in order to reduce the drive operating force in a gas circuit breaker, it is important to simplify the construction and reduce weight. For example, in the case of a series puffer type gas circuit breaker in which the puffer chamber is divided into two, since ancillary components such as the partition plate 10 and/or non-return valve 14 are indispensable, the construction tends to become more complicated and the weight of the moving parts tends to be increased. When the weight of the moving parts increases, a strong drive operating force is inevitably necessitated. In other words, in a conventional series puffer type gas circuit breaker, simplification of the construction is sought in order to contribute to reduction in weight of the moving parts.
(E) Direction of the Gas Flow
Furthermore, in a puffer type gas circuit breaker in which a gas blast 21 is directed onto an arc discharge 7, stabilization of the flow of arc-extinguishing gas 1 within the appliance is considered vital. In particular, in a series puffer type gas circuit breaker the flow of arc-extinguishing gas tends to become unstable, and improvement in this regard is desired.
Specifically, in a series puffer type gas circuit breaker, arc-extinguishing gas 1 that flows out from the compression puffer chamber 12 flows into the arc discharge 7 within the insulated nozzle 8 after passing through the heating puffer chamber 11. Consequently, the flow path area of the arc-extinguishing gas 1 from the compression puffer chamber 12 through the communication aperture 13 of the partition plate 10 until it reaches the arc discharge 7 is greatly expanded in the region of the heating puffer chamber 11 so smooth flow of arc-extinguishing gas 1 is impeded.
Furthermore, in the case of interrupting a small current, the pressure of the heating puffer chamber 11 is low, since the thermal energy of the hot exhaust gas 20 is small; the arc-extinguishing gas 1 that flows in from the compression puffer chamber 12 is thus consumed in elevating the pressure of the heating puffer chamber 11 until it reaches the same pressure as that of the compression puffer chamber 12. The pressure of the arc-extinguishing gas 1 when directed towards the arc discharge 7 was therefore very small, making it difficult to achieve superior interruption performance.
Also, in a series puffer type gas circuit breaker, when performing interruption in the large current region, the gas blast 21 is directed onto the arc discharge 7 solely by the pressure of the heating puffer chamber 11 whereas, when performing interruption in the small current region, the arc-extinguishing gas 1 from the compression puffer chamber 12 is directed onto the arc discharge 7. In other words, in the case of a series puffer type gas circuit breaker, the space supplying the arc-extinguishing gas 1 is changed over between the heating puffer chamber 11 and the compression puffer chamber 12 in accordance with the magnitude of the current that is to be interrupted.
The above changeover is effected by passive opening/closure of the non-return valve 14 in response to the pressure difference of the heating puffer chamber 11 and the compression puffer chamber 12. Consequently, in the intermediate current region, when the pressure difference between the heating puffer chamber 11 and the compression puffer chamber 12 is small, changeover of the source of supply of the arc-extinguishing gas 1 becomes indeterminate, and the operation of the non-return valve 14 thus becomes unstable. Thus, in spite of this action of the non-return valve 14, there was a risk that the flow of arc-extinguishing gas 1 would become unstable.
(F) Interruption Performance in the Case of High-Speed Re-Closure Action
Furthermore, while it is of course desirable that a gas circuit breaker should have excellent interruption performance in the case of high-speed re-closure action, there is the problem that poor interruption performance in high-speed re-closure action is sometimes experienced with series puffer type gas circuit breakers. Specifically, the inlet hole 17 and inlet valve 19 are formed in the fixed piston 15, so, during closure operation, albeit the arc-extinguishing gas 1 is replenished by intake therefrom in the case of the compression puffer chamber 12, in the case of the heating puffer chamber 11, no such intake replenishment of arc-extinguishing gas 1 is possible. As a result, the interior of the heating puffer chamber 11 immediately after a first occasion of current interruption is filled with arc-extinguishing gas 1 that has been heated to a high temperature by the high-temperature arc discharge 7.
Consequently, if a second current interruption is performed in a condition in which the gas within the heating puffer chamber 11 has not been replaced by arc-extinguishing gas 1 of low temperature and high density, high-temperature, low-density arc-extinguishing gas 1 will be directed onto the arc discharge 7. The arc-extinguishing performance and electrical insulation performance of high-temperature, low-density gas is poor. There was therefore concern that the interruption performance of a series puffer type gas circuit breaker would be degraded in the case of high-speed re-closure action.
The gas circuit breaker according to the present embodiment was proposed in order to solve all the problems described above. Specifically, an object of the gas circuit breaker according to this embodiment is to provide a gas circuit breaker wherein: the temperature of the gas blast is lowered; durability is improved and maintenance is reduced; the current interruption time is shortened; and the drive operating force is reduced; and, in addition, in which the flow of arc-extinguishing gas is stabilized, and, furthermore, the interruption performance during high-speed re-closure action is improved.
In order to achieve the above object, the following construction is provided according to the present invention. Specifically, a gas circuit breaker is characterized in that it is constituted by oppositely arranging a pair of arc electrodes in a sealed container filled with arc-extinguishing gas, said arc electrodes being constructed so that they are capable of electrical conduction and are capable of generating arc discharge between these two electrodes during current interruption, and is provided with:
a pressurizing means in order to direct arc-extinguishing gas onto said arc discharge, that generates pressurized gas by elevating the pressure of said arc-extinguishing gas;
a pressure-accumulation space that accumulates said pressurized gas; and
a flow-shaping means that directs said pressurized gas toward said arc discharge from said pressure-accumulation space;
said gas circuit breaker comprising:
a hot exhaust gas accumulation space that is provided in order to temporarily accumulate hot exhaust gas generated by the heat of said arc discharge; comprising a pressurized gas through-flow space communicating with said pressure-accumulation space, and an opening/closing section that can be freely opened/closed, provided in order to produce a closed condition or open condition of said pressure-accumulation space;
wherein said opening/closing section is constituted so that it is in a closed condition in the earlier half of the current interruption period, in which it prevents inflow of said hot exhaust gas into said pressure-accumulation space, and is in an open condition in the latter half of the current interruption period, so as to direct said pressurized gas in said pressure-accumulation space onto said arc discharge.